Unit Price Calculator

Enter the price and size of up to four products and choose a unit to compare by, such as price per ounce, per pound, per 100 grams, per liter or per item. The calculator converts every package to the same unit, including multipacks and mixed units like ounces against kilograms, and shows which one is the better value and by what percentage. A chart lays the unit prices side by side. It works for groceries, household supplies, fuel, building materials sold by length or area, and anything else sold in different sizes.

unit price = price ÷ (size × number of packs), converted to the unit you compare by

Sizes are converted with exact NIST factors: 1 ounce is 28.349523125 grams, 1 pound is 453.59237 grams and 1 US fluid ounce is 29.5735295625 milliliters. Weight can only be compared with weight and volume with volume, because converting between them needs the density of the product. The calculator tells you if units do not match.

Cereal. A 16 oz box at $3.99 costs $0.249 per ounce; a 24 oz box at $5.49 costs $0.229. The larger box is 8.3% cheaper per ounce.

Soda. Twelve 12 fl oz cans at $6.99 hold 4.26 liters, $1.64 per liter, while a 2 liter bottle at $2.49 is $1.25 per liter. The bottle is cheaper per liter, though cans may suit you better if a bottle goes flat before it is finished.

Many US stores print a unit price on the shelf tag, and some states require it. NIST's model unit pricing regulation recommends consistent units for each product type, such as price per ounce for cereal or per 100 count for tissues, but stores do not always follow it, and a tag may show one size per ounce and the next per pound. Comparing them by eye then leads to mistakes. Enter both here to compare like with like.

Usually, but not always. Sales on small sizes, store brands and multipack pricing often reverse the pattern, and researchers who study grocery prices have documented quantity surcharges, where the larger package costs more per unit. Check the unit price rather than assuming. Also consider whether you will use it all: a bulk pack that partly goes to waste can cost more per unit actually used than a small one, and storage space has a cost too.

Manufacturers sometimes reduce the contents of a package while keeping the price and the look the same, a practice often called shrinkflation. The price on the shelf does not change, but the unit price rises. Keeping a note of the unit price of products you buy often, and comparing it with this calculator when the package looks different, makes these changes easy to see.

• Compare the same product quality. Unit price shows cost, not taste, freshness or ingredients.
• For concentrated products, such as laundry detergent, compare price per load or per use rather than per ounce, using the count unit.
• Include coupons and loyalty discounts by entering the price you will actually pay.
• For drained products such as canned fruit, the label's net weight includes the liquid; the drained weight is a fairer basis if it is listed.